The present invention relates generally to printing presses and more particularly to a folder of a printing press.
Web printing press print a continuous web of material, such as paper. In a folder of the web printing press, the continuous web then is cut into signatures in a cutting unit and folded.
U.S. Pat. No. 5,429,578 describes a jaw folder receiving a web of material. A cutting cylinder, transfer cylinder and jaw cylinder are provided. The web is cut by the transfer cylinder where the lead edge of the signature is secured by pins. The signature is thus held on the transfer cylinder until tucking blades on the transfer cylinder tuck the signatures into jaws of the jaw cylinder. Thus a cross-fold on the signatures is created along a fold line perpendicular to the travel direction of the signatures. The signatures are then held by the jaws at the fold line until the signatures are to be released. In order to change the position of the fold with respect to the lead edge, the position of the tucking blade with respect to the pins is changed.
FIG. 1 shows details of a known transfer cylinder for a gripper folder, which is type of jaw folder having grippers instead of pins. Tucking blades 12 are supported on a spider 12 geared to a drive shaft. Grippers 20 for lead edges of the signatures 5 are supported on a spider 14, which is also supported on the drive shaft and which normally rotates with spider 12. However, spider 14 is rotatable with respect to spider 12, so that the fold location 15 can be changed.
The signature 5 is supported by cantilevered support segments 18 and 19 attached to spider 12 and supports 21 attached to spider 14. However, in order to provide for relative adjustment of spider 12 with respect to spider 14, gaps 8 and 9 are provided between the cantilevered segments. These gaps 8, 9 have respective clearances d, e which define the amount of relative adjustment possible between the spiders 12, 14.
If large cross-fold adjustment is desired, the gaps in the transfer cylinder must be rather large, which can lead to a lack of support for signatures that in turn can lead to defects such as creasing, edge-tearing or dog-earring. The cantilevered support segments also may be prone to damage from jam forces, which can cause them to bend or break off.
Particularly in the field of newspaper presses, it has been known to provide rotary blade folders, also known as drum folders, that tuck a thick newspaper signature into two nip rollers. U.S. Pat. No. 5,122,109 discloses such a rotary blade folder. The rotary blade passes through bands at the outer surface of the cylinder. Pins for the lead edge of the signature pass through an axially extending gap of the cylinder. In newspaper rotary blade folders of this type it is desirable to adjust the effective radius of the bands to accommodate different signature thicknesses, and thus the bands are located at the tucking blades.
Commonly-assigned U.S. Ser. No. 09/571,606 (which is not necessarily prior art to the present invention) describes a rotary blade folder with an expansion plate with apertures that permit the rotary blades to pass therethrough, and permits adjustment of the effective diameter of the cylinder. The pins remain exposed. The newspaper rotary blade folders do not interact with a jaw cylinder.
Also, in rotary blade or drum folders, the tucking blades typically are supported on an interior cylinder with a planetary gear and then pass through bands, so that the gap problem mentioned with respect to jaw folders often does not exist.